Electrodeposition of copper from acid baths

ABSTRACT

A bath for electrodepositing ductile, lustrous copper which comprises an aqueous acidic copper plating bath containing dissolved therein a brightening amount of the reaction product of polyethyleneimine and an alkylating agent which will alkylate the nitrogen of the polyethyleneimine to produce a quaternary nitrogen, wherein the reaction temperature for the imine and alkylating agent ranges from about room temperature to about 120*C and the reaction product is present in the bath in an amount from about 0.1 to 1,000 milligrams per liter.

United States Patent Creutz Nov. 6, 1973 [54] ELECTRODEPOSITION OFCOPPER FROM 3,328,273 6/l967 Creutz et al 204/52 R A I BATES 3,393,1357/1968 Rosenberg 3,502,551 3/1970 Todt et al. 1 lnventorl ga g- Creutz,Westland, 3,542,655 11/1970 Kardos et al 204 52 R FOREIGN PATENTS ORAPPLICATIONS 1 Ass1gnee= Y Metal Finishing Corporation, 1,515,363 3/1968France 204 52 R Warren, Mlch. [22] Filed; Jam 21 1972 Primary ExaminerG.L. Kaplan Att0rney-William J. Schramm 211 Appl. No.: 219,845

Related u.s. Application Data 1 ABSTRACT [63] Continuation-impart ofSer. No. 11,024, Feb. 12, A bath for electrodeposlting ductile lustrouspp 1970, b d d, which comprises an aqueous acidic copper plating bathcontaining dissolved therein a brightening amount of [52] 0.8. CI 204/52R h i n pr c f polye hyleneimine and an al- [51] Int. Cl. C23b 5/20,C23b 5/46 y g agent whi will alkyl te the nitrogen of the [58] Field ofSearch 204/52 R, 44, 106, polyethyleneimine to produce a quaternarynitroge 204/107, 108; 106/1; 117/130 E wherein the reaction temperaturefor the imine and alkylating agent ranges from about room temperature to[56] R fere s Cit d about 120C and the reaction product is present inthe UNITED STATES PATENTS bath in an amount from about 0.1 to 1,000milligrams 2,853,444 9/1958 Pye et al. 204/108 per 3,267,010 8/1966Creutz et al. 204/52 R 12 Claims, N0 Drawings ELECTRODEPOSITION OFCOPPER FROM ACID BATHS CROSS REFERENCE TO RELATED APPLICATION Thisapplication is a continuation-in-part of Ser. No. 11,024, filed Feb. 12,1970, now abandoned.

This invention relates to the electrodeposition of copper from aqueousacidic plating baths, especially from copper sulfate and fluorobo'r'atebaths, and more particularly it relates to the use of certain organiccompounds in the baths to give bright, highly ductile, low

stress, good leveling copper deposits over a wider range of bathconcentration and operating current densities.

I-leretofore, numerous additives have been proposed for use in aqueousacidic plating baths for the electrodeposition of copper. For example,in US. Pat. Nos. 3,267,010 and 3,328,273, it is proposed to usebathsoluble polyether compounds, including those which are polymers of1,3-dioxalane, in combination with various organic sulfide compounds,including organic sulfides which contain at least one sulfonic group andaliphatic polysulfide compounds. Although bright, ductile copperelectrodeposits are produced from these baths containing these organicadditives, in some instances the deposits formed have poor levelingcharacteristics and in low current density areas a dull plate may beproduced. Accordingly, these patents further disclose the desirabilityof utilizing, in addition to the polyether and organic sulfide compoundsa phenazine dye, such as diethyl or dimethyl Safranine Azo dimethylaniline. With the addition of such dye materials full bright, leveledcopper deposits are obtained.

See also French Patent 1,515,363 which describes the use of alkylatedpolyethyleneimine in copper plating solutions.

While these bright, ductile leveling copper plating baths are in largecommercial use, nevertheless an important improvement would be the useof higher bath temperatures without causing excessive dulling of theplate. Even a 5F increase in the optimum bath temperature for brightplate would allow a very significant increase in the current densityused and thus in the speed of plating. With higher speed plating,shorter plating time can, of course, be used, thus allowing greater.production with a given volume of plating solution.

It has now been found that the reaction product of polyethyleneiminewith benzyl chloride or similar reactive organic halogen compounds arebrightening additives in the acid copper plating baths, and can beemployed instead of phenazine dyes with definite improvements. Theseimprovements constitute the main objects of this invention, and are herelisted:

1. An object of the present invention is to provide an improved processfor the electrodeposition of copper from an aqueous acidic copperplating bath, by making possible the use of higher bath temperatureswithout causing excessive dulling of the plate.

2. Another object of this invention is to provide an improved brightplating acid copper bath that provides smooth anode dissolution (lessloose particles than normal.

3. A further object of the present invention is to provide an improvedaqueous acidic bath for the electrodeposition of bright leveling,ductile, copper deposits over a wider bath temperature range withoutexcessive dulling of low current density areas while still makingpossible brilliant plate at the highest current density ranges. I

These and other objects will become apparent to those skilled in the artfrom the description of the invention which follows.

Pursuant to the above objects, the present invention includes a bath forelectrodepositing ductile, lustrous copper which comprises an aqueousacidic copper plating bath which contains a brightening amount of amaterial which is the reaction product of polyethyleneimine and anorganic compound which will alkylate the nitrogen in thepolyethyleneimine. By the use of such additives, particularly when usedin conjunction with organic sulfide compounds and bath soluble polyethercompounds, full bright, leveled copper deposits, are obtained, alongwith better anode dissolution and improved adhesion of subsequentlyapplied plates, over a wide range of operating temperatures, currentdensities and bath concentrations.

More specifically, in the practice of the present invention, the aqueousacidic copper plating baths conthe additive materials for use in thepresent acid copper plating baths. In this regard, it is to be notedthat the alkylation may take place at the primary, secondary and/ortertiary nitrogen of the polyethyleneimine and that the number ofnitrogen atoms of each type will vary, depending upon the amount ofbranching present in the polyethyleneimine.

When the alkylating agent reacts with the primary or secondary amine, itwill be altered to the secondary and tertiary amine, respectively. Thisis accomplished by adding more alkylating agent as is desired. Where thealkylation takes place at the primary and/or secondary nitrogen, therewill be a splitting off of the alkylating groups on the organiccompound, e.g., halogen, sulfate, or the like. In the case of thetertiary nitrogen, however, a quatemization takes place, forming thequaternary salt.

It is preferred that as many nitrogen atoms as possible in thepolyethyleneimine brightener should be quaternized, although as littleas 5 percent of the nitrogen atoms being quaternary still givesdesirable results, with 10% being more preferred and even morepreferably alkyl sulfates, alkyl sultones, aldehydes, ketones,isocyanates, thioisocyanates, epoxides, acylamindes, acids, anhydrides,ureas, cyanamides, guanidines, and the like, may also be used. It is tobe appreciated that in some instances organic compounds may be used inwhich the reacting group is attached directly to an aromatic nucleus,rather than on an alkyl chain. Exemplary of such materials is2,4-dinitrochlorobenzene, which will react with either the primary orsecondary nitrogen of the polyethyleneimine and/or will quaternize withthe tertiary nitrogen. Accordingly, in referring to the alkylation ofthe nitrogen in the polyethyleneimine, it is intended to include thosecases in which the nitrogen is attached directly to an aryl or aromaticnucleus, as well as those in which it is attached to an aliphatic group.Specific compounds which have been found to give particularly goodresults are benzyl chloride, allyl bromide, dimethyl sulfate, andpropane sultone. These compounds, however, are merely exemplary of theorganic compounds which will alkylate the nitrogen of thepolyethyleneimine. Preferably the alkylating agent is an aromatichalide.

In reacting the polyethyleneimine with the organic alkylating compound,to form the additive composition for the acid copper plating baths ofthe present invention, an excess of the organic alkylating compound,over the theoretical amount required to completely react with thepolyethyleneimine, is preferred. While an excess of the alkylating agentis preferred excellent results are also obtained with lesser degrees ofalkylation. This reaction may be carried out by admixing thepolyethyleneimine and the organic alkylating compound, either with orwithout a solvent. Illustrative of solvents which may be used isdioxane. The reaction temperature may vary from about room temperatureto about 120 C, although where a solvent such as dioxane is used,reaction temperatures of from about 80 to 100C are preferred. Theresulting reaction product is then separated from any unreactedmaterials, using any convenient techniques. It is to be appreciated thatalthough it is preferred to use an excess of the organic alkylatingcompound, so that substantially complete alkylation of the nitrogen inthe polyethyleneimine is effected, this has not been found to beessential. In many instances, greatly improved plating results have beenobtained when using a polyethyleneimine which is only partially orincompletely alkylated.

The polyethyleneimine which is used in forming the plating bath additivemay have a wide range of molecular weights. Typically, the molecularwieght of the polyethyleneimine may be within the range of about 300 toseveral millions. In many instances, however, molecular wieghts withinthe range of about 300 to 1,000,000 are preferred.

In addition to the above described brightening agent, the aqueous acidcopper plating baths of the present invention also desirably contain atleast one bathsoluble polyether compound. Various polyether compoundswhich are soluble in the plating bath may be used. For example,particularly in high sulfuric acid and low copper metal baths, non-ionicpolyether wetting agents, such as polyglycols having carbon chainsgreater than 6 in length, may be useful. In general, however, the mostpreferred polyethers are those containing at least six ether oxygenatoms and being free from alkyl chains having more than six carbon atomsin a straight or branched chain. Of the various polyether compoundswhich may be used, excellent results have been obtained with thepolypropylene propanols and glycols of average molecular weight of fromabout 360 to 1000, i.e., polyethers which contain a group (C H O where yis an integer of from about 6 to 20. Excellent results have also beenobtained with polyethers containing the group (C H.,O) where x is aninteger of at least 6. Exemplary of the various preferred polyethercompounds which may be used are those set forth in Table II appearing incolumns 5 and 6 of U.S. Pat. No. 3,328,273. Desirably, the plating bathsof the present invention contain these polyether compounds in amountswithin the range of about 0.01 to 5 grams per liter, with the lowerconcentrations generally being used with the higher molecular weightpolyethers.

In addition to the polyethyleneimine reaction prodnet and the polyethercompound, the aqueous acidic copper plating baths of the presentinvention also desirably contain an organic sulfide compound. Typical ofthe suitable organic sulfides which may be used are sulfonated organicsulfides, i.e., organic sulfide compounds carrying at least one sulfonicgroup. These organic sulfide sulfonic compounds may also contain varioussubstituting groups, such as methyl, chloro, bromo, methoxy, ethoxy,carboxy and hydroxy, on the molecules, especially on the aromatic andheterocyclic sulfide sulfonic acids. The organic sulfide sulfonic acidmay be used as the free acids, the alkali metal salts, organic aminesalts, or the like. Exemplary of specific sulfonate organic sulfideswhich may be used are those set forth in Table I in columns 5 and 6 andcolumns 7 and 8 of U.S. Pat. No. 3,267,010,0ther suitable organicsulfide compounds which may be used are mercaptans, thiocarbamates,thiolcarbamates, thioxanthates, and thiocarbonates which contain atleast one sulfonic group. Additionally, organic polysulfide compound mayalso be used. Such organic polysulfide compounds may have the formulaXR,-(S)n-R -SO H, wherein R and R are the same or different alkylenegroup containing from about 1 to 6 carbon atoms, X is hydrogen or SO Hand n is a number from about 2 to 5. These sulfide compounds arealiphatic polysulfides wherein at least two divalent sulfur atoms arevicinal and wherein the molecule has one or two terminal sulfonic acidgroups. The alkylene portion of the molecule may be substituted withgroups such as methyl, ethyl, chloro, bromo, ethoxy, hydroxy and thelike. These compounds may be added as the free acids or as the alkalimetal or amine salts. Exemplary of specific organic polysulfidecompounds which may be used are set forth in Table I of column 2 of U.S.Pat. No. 3,328,273. Desirably, these organic sulfide compounds arepresent in the plating baths of the present invention in amounts withinthe range of about 0.0005 to 1.0 grams per liter. The copper platingbaths in which the above additives are used may be either acidic coppersulfate or acidic copper fluoroborate baths. As is known in the art,such acidic copper sulfate baths typically contain from about 180 to 250grams per liter of copper sulfate and 30 to grams per literof sulfuricacid; while the acidic copper fluoroborate baths typically contain fromabout 200 to 600 grams per liter of copper fluoroborate and about 0 to60 grams per liter of fluoroboric acid. Additionally, it is found thatwith the additives of the present invention, these acid copper platingbaths may be operated under conditions of high acid and low metalcontent. Thus, even with plating baths which contain as little as about7.5 grams per liter copper and as much as 350 grams per liter sulfuricacid or 350 grams per liter of fluoroboric acid, excellent platingresults are still obtained.

Desirably, these plating baths are operated at current densities withinthe range of about 10 to amps per square foot, although, in manyinstances, current densities as low as about 0.5 amps per square footmay also be used. Typically, with low copper and high acid baths,current densities within the range of about to 50 amps/ft are used.Additionally, in high agitation baths, such as those used in platingrotogravure cylinders, current densities up to as high as about 400amps/ft may be used. The baths may be operated with air agitation,cathode-rod agitation, or solution agitation and cathode rod agitation,depending upon the particular bath and plating conditions which areused. Typical bath temperatures are within the range of about to C,although both lower and higher temperatures, e.g., 50 C or more, mayalso be used. In this regard, it is to be noted that the plating bathsof the present invention mayalso be used in copper electrorefiningprocesses. In such processes, temperatures up to about 6070C may beused.

Although it has been found to be desirable that chloride and/or bromideanions in the bath are below about 0.1 gram per liter, appreciablygreater amounts of many inorganic cations, such as ferrous iron, nickel,cobalt, zinc, cadmium, and the like, may be present in the bath, e.g.,amounts at least as high as about 25 grams per liter, withoutdetrimental effect. It has further been found that not only do the acidcopper plating baths of the present invention give excellent resultswhen used under conditions of high acid and low copper metal content,but, additionally the baths have been found to be particularly welladapted for throughhole plating, and thus find appreciable utilizationin the manufacture of printed circuit board.

In order that those skilled in the art may better understand the presentinvention and the manner in which it may be practiced, the followingspecific examples are given. In these examples, unless otherwiseindicated, parts and percent are by weight and temperatures are indegrees centigrade.

EXAMPLE 1 An aqueous acidic copper electroplating bath was formulatedcontaining the following components in the amounts indicated:

ounces per gallon Copper metal (from CuSO.5H,O) 2

H 80 (100%) 30 parts per million I'ICl (100%) 30 S-(CHz) s-SOaH Insteadof the thioxanthate sulfonic acid, the disulfide alkyl sulfoniccompounds such as HO S-(Cl-l -S- S-(CH,),,-SO ,H can be used.

EXAMPLE 2 An aqueous acidic copper electroplating bath was formulatedcontaining the following components in the amounts indicated:

ounces per gallon Copper metal (from Cu(BF 2 HBF,( l00%) 20 H 80, l

CH3 S-S- -GHa -S0sH 20 parts per million Polyethylene glycol (molecularweight 6000) Reaction product of polyethyleneimine (molecular weightabout 1200) with benzyl chloride (in molar ratios). The imine reactantcontained about 25% primary nitrogen; 50% secondary and 25% tertiarynitrogen. l-lCl EXAMPLE 3 An aqueous acidic copper electroplatingsolution was formulated containing the following components in theamounts indicated:

with allyl bromide (in molar ratios The amine reactant contained about25% primary nitrogen; 50% secondary and 25% tertiary nitrogen Theaqueous acidic copper plating baths of the preceding Examples 1 through3 were operated using air agitation at an average current density ofabout 40 amps per square foot and a temperature of about 25 C. In eachinstance, full bright, leveled copper plates were obtained on thecathode and the anodes were evenly corroded on the surface.

The procedure of the preceding Examples 1-3 is repeated with theexception that in the preparation of the polyethyleneimine reactionproduct, propane sultone and dimethylsulfate are substituted for thebenzyl chloride and the allyl bromide. In each instance, operation ofthe resulting plating bath produces full bright, leveled copper plate onthe cathode and even surface corrosion of the anode.

EXAMPLE 4 Acid copper electroplating solutions are prepared as inExamples 1-3 with the exception that the solutions contained 40grams/liter copper grams/liter CuSO .5l-l O) and 12 percent by volume H804. These baths are used for copper electrorefining at currentdensities of 20 to 40 amps/ft and temperatures of 55 to 65C. In eachinstance a smooth, pure copper plate is obtained.

While there have been described various embodiments of the invention,the compositions and methods described are intended to be understood aslimiting the scope of the invention as it is realized that changestherewithin are possible and it is further intended that each elementrecited in any of the following claims is to be understood as referringto all equivalent elements for accomplishing substantially the sameresults in substantially the same or equivalent manner, it beingintended to cover the invention broadly in whatever form its principlemay be utilized.

What is claimed is:

l. A bath for electrodepositing ductile, lustrous copper which comprisesan aqueous acidic copper plating bath containing dissolved therein abrightening amount of the reaction product of polyethyleneimine and analkylating agent which will alkylate the nitrogen on thepolyethyleneimine to produce a quaternary nitrogen, said alkylatingagent being selected from the group consisting of benzyl chloride, allylbromide, propane sultone, and dimethyl sulfate, and wherein the reactiontemperature for the imine and alkylating agent ranges from about roomtemperature to about 120C and the reaction product is present in thebath in an amount ranging from about 0.1 to 1,000 milligrams per liter.

2. The bath as claimed in claim 1, wherein there is also present a bathsoluble polyether compound and an organic sulfide compound selected fromaliphatic polysulfides and organic sulfides carrying at least onesulfonic group.

3. The bath as claimed in claim 2, wherein the polyethyleneiminereaction product is present in an amount within the range of about 0.1to 1,000 milligrams per liter, the polyether compound is present in anamount within the range of about 0.01 to grams per liter and the organicsulfide compound is present in an amount within the range of about0.0005 to 0.1 grams per liter.

4. The bath as claimed in claim 3, wherein the reaction product isformed by the reaction of polyethyleneimine and benzyl chloride, thepolyether is polypropylene glycol and the organic sulfide is HO S(CH-S-S- 5. The bath of claim 1, wherein the alkylating agent is benzylchloride.

6. The bath of claim 1, wherein the alkylating agent is allyl bromide.

'7. A method for electrodepositing a ductile, lustrous copper whichcomprises the step of electrodepositing copper from an aqueous copperplating bath containing dissolved therein a brightening amount of thereaction product of polyethyleneimine and an alkylating agent which willalkylate the nitrogen, said alkylating agent being selected from thegroup consisting of benzyl chloride, allyl bromide, propane sultone, anddimethyl sulfate, and wherein the reaction temperature for the imine andalkylating agent ranges from about room temperature to about C and thereaction product is present in the bath in an amount from about 0.1 to1,000 milligrams per liter.

8. The method as claimed in claim 7, wherein the plating bath alsocontains a bath-soluble polyether compound and an organic sulfidecompound selected from aliphatic polysulfides and organic sulfidecompounds carrying at least one sulfonic group.

9. The method as claimed in claim 8, wherein the polyethyleneiminereaction product is present in the bath in an amount within the range ofabout 0.1 to 1,000 milligrams per liter, the polyether compound ispresent in the bath in an amount within the range of about 0.01 to 5grams per liter and the organic sulfide compound is present in the bathin an amount within the range of about 0.0005 to 1.0 grams per liter.

10. The method as claimed in claim 9, wherein the reaction product isformed by the reaction of polyethyleneimine and benzyl chloride, thepolyether compound is polypropylene glycol, and the organic sulfidecompound is HO S-(CH -S-S-(CH );,SO H.

11. The method of claim 7, wherein the alkylating agent is benzylchloride.

12. The method of claim 7, wherein the alkylating agent is allylbromide.

2. The bath as claimed in claim 1, wherein there is also present a bathsoluble polyether compound and an organic sulfide compound selected fromaliphatic polysulfides and organic sulfides carrying at least onesulfonic group.
 3. The bath as claimed in claim 2, wherein thepolyethyleneimine reaction product is present in an amount within therange of about 0.1 to 1,000 milligrams per liter, the polyether compoundis present in an amount within the range of about 0.01 to 5 grams perliter and the organic sulfide compound is present in an amount withinthe range of about 0.0005 to 0.1 grams per liter.
 4. The bath as claimedin claim 3, wherein the reaction product is formed by the reaction ofpolyethyleneimine and benzyl chloride, the polyether is polypropyleneglycol and the organic sulfide is HO3S(CH2)3-S-S-(CH2)3-SO3H.
 5. Thebath of claim 1, wherein the alkylating agent is benzyl chloride.
 6. Thebath of claim 1, wherein the alkylating agent is allyl bromide.
 7. Amethod for electrodepositing a ductile, lustrous copper which comprisesthe step of electrodepositing copper from an aqueous copper plating bathcontaining dissolved therein a brightening amount of the reactionproduct of polyethyleneimine and an alkylating agent which will alkylatethe nitrogen, said alkylating agent being selected from the groUpconsisting of benzyl chloride, allyl bromide, propane sultone, anddimethyl sulfate, and wherein the reaction temperature for the imine andalkylating agent ranges from about room temperature to about 120*C andthe reaction product is present in the bath in an amount from about 0.1to 1,000 milligrams per liter.
 8. The method as claimed in claim 7,wherein the plating bath also contains a bath-soluble polyether compoundand an organic sulfide compound selected from aliphatic polysulfides andorganic sulfide compounds carrying at least one sulfonic group.
 9. Themethod as claimed in claim 8, wherein the polyethyleneimine reactionproduct is present in the bath in an amount within the range of about0.1 to 1,000 milligrams per liter, the polyether compound is present inthe bath in an amount within the range of about 0.01 to 5 grams perliter and the organic sulfide compound is present in the bath in anamount within the range of about 0.0005 to 1.0 grams per liter.
 10. Themethod as claimed in claim 9, wherein the reaction product is formed bythe reaction of polyethyleneimine and benzyl chloride, the polyethercompound is polypropylene glycol, and the organic sulfide compound isHO3S-(CH2)3-S-S-(CH2)3SO3H.
 11. The method of claim 7, wherein thealkylating agent is benzyl chloride.
 12. The method of claim 7, whereinthe alkylating agent is allyl bromide.